This invention relates to a control apparatus for a fuel injector of an automotive engine. More particularly, it relates to a control apparatus which can properly control the supply of fuel to a fuel injector even when there are variations in the discharge pressure of a fuel pump which supplies fuel to the fuel injector.
A controller for an electronic fuel injection valve (hereinbelow referred to as a fuel injector) of an automobile engine turns the fuel injector on and off by the application thereto of electronic pulses having a prescribed pulse width. In a conventional controller the pulse width is determined on the basis of the engine rotational speed, the intake manifold pressure, and other parameters of engine operation.
Recently, in-tank fuel supply systems which have a turbine-type pump housed inside a fuel tank are becoming common since they reduce the noise which is generated by the fuel pump. The fuel pump is powered by the battery of the automobile. When the battery voltage falls, the discharge pressure of a turbine-type fuel pump correspondingly decreases.
The discharge pressure of a fuel pump is also affected by the temperature of the fuel. Namely, a decrease in the fuel temperature causes an increase in the viscosity of the fuel, which causes the discharge pressure of the fuel pump to drop. Accordingly, when the battery voltage and the fuel temperature decrease to certain values, the discharge pressure of the fuel pump will fall below a level at which the fuel pressure can not be maintained at its normal level, such as 2.55 kg/cm.sup.2.
In a conventional fuel injector controller, the pulse width of the pulses which are applied to the fuel injector are not corrected for the decrease in the fuel pressure resulting from a decrease in the battery voltage or the fuel temperature. Therefore, at times when the fuel pressure falls below its normal level due to a decrease in the battery voltage or the fuel temperature, such as when the engine is first started, the proper amount of fuel can not be supplied to the engine by the fuel injector.